Guidewires are used in numerous catheterization procedures as an aid to placement of a catheter at a selected site within the human body. The catheter is constructed to perform a particular procedure at that internal site. Among the more common uses of guidewires is in the catheterization of blood vessels for diagnostic or therapeutic purposes. In a common type of vascular catheterization procedure, the guidewire first is inserted, usually percutaneously, into one of the patient's blood vessels and is manipulated and advanced through the branches of the vascular system to the target site. The catheter then is threaded over and advanced along the guidewire, with the guidewire serving to guide the catheter directly to the target site.
By way of further example, a number of catheterization procedures are performed with respect to the coronary arteries. In one such procedure for diagnostic purposes, an angiographic catheter is advanced through the patient's arteries to the entrance to the coronary arteries. A radiopaque contrast liquid then is injected through the angiographic catheter into the coronary arteries under X-ray fluoroscopy, so that the anatomy of the patient's coronary arteries may be observed visually. Once the coronary anatomy has been determined, the physician may perform additional catheterization procedures, including percutaneous transluminal coronary angioplasty (PTCA), in which a balloon catheter or other angioplasty catheter is advanced into the coronary arteries to widen an obstructed portion (stenosis) of the artery.
In a typical PTCA procedure, an angioplasty catheter, which may be in the form of an elongate flexible shaft with an inflatable balloon at its distal end, is advanced from the percutaneous puncture site in the patient's femoral artery through the patient's arteries toward the heart and into the coronary arteries. The catheter is guided to the target site of the obstruction by use of a slender guidewire which initially is advanced into and manipulated through the coronary arteries in advance of the dilatation catheter. Once the distal end of the guidewire is in place within the obstruction, the catheter then is advanced over the guidewire which guides the catheter directly to the obstruction to place its balloon within the obstruction. The balloon then is inflated to dilate the obstructed portion of the artery, thereby enlarging the flow area through the artery.
Guidewires used with PTCA catheters are of special design. Although they are extremely slender, of the order of 0.010 to 0.018 inches in diameter, they nevertheless must be capable of transmitting rotation from the proximal end of the guidewire to the distal end in order that the physician may controllably steer the guidewire through the branches of the patient's arteries and manipulate it to the target site in the intended coronary artery. Additionally, the distal end of the guidewire must be sufficiently flexible in order that the distal portion of the guidewire can pass through sharply curved tortuous coronary anatomy as well as to provide a sufficiently soft, distal tip that will not injure the artery or its delicate inner lining. It also is among the desirable features of a guidewire that it have sufficient column strength so that it can be pushed without buckling.
Among the common guidewire configurations used in angioplasty is the type of guidewire illustrated in U.S. Pat. No. 4,545,390 (Leary). Such a wire includes an elongate flexible shaft, typically formed from stainless steel, having a tapered distal portion and a helical coil mounted to and about the tapered distal portion. The generally tapering distal portion of the shaft acts as a core for the coil and results in a guidewire having a distal portion of increasing flexibility that is adapted to follow the contours of the vascular anatomy while still being capable of transmitting rotation from the proximal end of the guidewire to the distal end so that the physician can controllably steer the guidewire through the patient's blood vessels. The characteristics of the guidewire are affected significantly by the details of construction as the distal tip of the guidewire. For example, in one type of tip construction, the tapering core wire extends fully through the helical coil to the distal tip of the coil and is attached directly to a smoothly rounded tip weld at the distal tip of the coil. Such a construction typically results in a relatively stiff tip suited particularly for use when attempting to push the guidewire through a tight stenosis. In addition to a high degree of column strength, such a tip also displays excellent torsional characteristics.
In another type of tip construction, the tapered core wire terminates short of the tip weld. It is common in such a construction to attach a very thin metallic ribbon at one (proximal) end to the core wire and at its other (distal) end to the tip weld. The ribbon serves as a safety element to maintain the connection between the core wire and the distal tip weld in the event of coil breakage. It also serves to retain a bend formed in the ribbon to maintain the tip in a bent configuration as is desirable when manipulating and steering the guidewire. Additionally, by terminating the core wire short of the tip weld, the segment of the helical coil between the distal end of the core wire and the tip weld is very flexible and floppy. The floppy tip is desirable in situations where the vasculature is highly tortuous and in which the guidewire must be capable of conforming to and following the tortuous anatomy with minimal trauma to the blood vessel.
In another type of tip construction, the distal-most segment of the core wire is hammered flat (flat-dropped) so as to serve the same function as the shaping ribbon but as an integral unitary piece with the core wire. The tip of the flat dropped segment is attached to the tip weld.
Although each of the above-described tip constructions has its advantages, each also presents some compromises and difficulties. Although the construction in which the core extends fully to and is attached to the tip weld is suited particularly for crossing a very tight stenosis, it may be unsuitable in those instances where a more tortuous anatomy with a less restrictive stenosis is encountered. Among the difficulties presented with the floppy type of tip construction is that the relatively poor column strength of the distal tip sometimes causes the floppy tip to prolapse, that is, to buckle and fold back on itself. For example, when the guidewire is negotiating tortuous anatomy, the physician may have been successful in maneuvering a portion of the guidewire tip partially into a particularbranch artery. With the very floppy distal tip, however, it sometimes occurs that when the physician pushes on the guidewire, the relatively poor column strength of the distal tip causes it to prolapse so that the trailing, stiffer portion of the guidewire does not follow into that branch but, instead, tends to advance straight ahead. That, in turn, pulls the portion of the tip that had entered the branch artery out of the branch artery. That may result in prolapse of the wire and, in the worst case, the formation of a permanent kink in the tip of the guidewire which destroys the steerability of the guidewire, thus rendering it unsuitable for further use. Consequently, it may become necessary to remove the guidewire, reshape it or replace it with an undamaged guidewire.
It would be desirable, therefore, to provide a tip construction for a guidewire which is sufficiently floppy so as to be atraumatic and follow the contour of tortuous anatomy, which displays good torque transmission to facilitate steering yet also provides improved column strength to reduce the risk of prolapse of the distal tip of the guidewire. It is among the general objects of the invention to provide such an improved guidewire tip construction.